Abstract: With the technique development of the governor system, the influence of governor system on low frequency oscillations（LFOs） has attracted more and more attention. The current research shows that the governor system not only can influence the damping characteristics of LFOs, but also will introduce a special very low frequency mode into the power system. This mode, called by frequency mode, has lower frequency than LFOs and would appear when the governor system is performed. In this paper, the influence of governor system on the damping characteristics of LFOs was investigated by using the torque analysis theory. Then the feature of the frequency mode and its influence on LFOs were mainly analyzed base on a 4-machine 2-area system. The analysis results show that frequency mode is a control mode of governor system and its damping ratio is significantly influenced by the parameters of the governor proportional integral derivative（PID） controller. When the governor system makes the damping ratios of LFOs become negative and the dead band is taken into account, the system LFO will gradually become equispacing oscillation if the damping ratio of the frequency mode is relatively strong, while the power LFO will appear like a beat frequency oscillation if the damping ratio of the frequency mode is relatively weak. Finally, simulation results of a practical inter-connected power system validate the effectiveness of the analysis results above.